Writing and painting on walls shows some of the oldest, most public forms of expression. Banksy, probably the most popular anonymous graffiti artist today, said that “a wall is a very big weapon. It’s one of the nastiest things you can hit someone with.” And during an event as big as the Olympic games that are concluding today in London as this is posted, that power is greatly magnified, causing conflict between artists and authorities.

Many in the graffiti community, including Banksy himself, have been adorning London’s walls with political statements and jokes about the international event. One rendering by the anonymous artist Mau Mau shows a beat-up Ronald McDonald, carrying the torch and leaving a trail of smoke and money. Meanwhile, Banksy portrays an athlete throwing a missile instead of a javelin. Another piece by Teddy Baden, called “Going for Gold,” shows a dog humping the one-eyed Olympic mascot.

London authorities have not taken the mockery lightly. According to The Atlantic Wire they’ve warned that any graffiti in the capital will be erased. There have also been numerous arrests by the British Transport Police that have been called by some graffiti artists a “crack down on graffiti.” Through mid-July, before the games began, the Transport Police confirmed four arrests for suspicion of conspiracy to commit criminal damage.

One of those arrested was Darren Cullen, who has been working legally as an artist for the past two decades. In an interview, Cullen, who also goes by the street name of SER, mentioned some of the conditions of bail imposed by the police. The conditions point to the real reasons for the arrests: he was banned from using railway services and from being within a mile of any Olympic venue until November.

Various voices (and spray cans) have reacted against the crackdown. The Banksy piece of the missile throwing competitor was made public in late July as a way to challenge authorities. Baden defended his work by saying that “it’s a quite British thing to kind of take the mick (poke fun) a bit.”

One of the strongest defenses came from art critic Jonathan Jones of The Guardian. He stated that graffiti is part of the very identity of London, and its grittiness is part of what attracts people to the city. “Tourists don’t come to London for shining perfection. They come for old and new in chaotic ungainly juxtaposition. And they come, partly, for Banksy…,” he stated.